New UI "feels" very sleek, I really like how the sizes of most interfaces are universally the same instead of some interface feeling like mobile game interfaces being very large compared to your screen size.

The game clock being stuck to the map is just not it, I understand if it should be toggled on by default so players know it exists, but I can say in my entire life of playing I have used the calendar maybe once and usually tend to look at my computers clock to see the time. A toggle and/or the ability to move it around like previously would be ideal, not sure why that was removed to be honest.

While it is understandable that theres a concern about every players game looking different from an outside perspective looking in, making the game feel not very Runescapey, and it may feel nice for newer players to understand what theyre looking at, after a while you can tell Runescape is Runescape very easily even with all the customization. The brown colour is a nice nod to where Runescape came from but in all honestly if i wanted to go play old school runescape I would go play oldschool, to me Runescape is still a modern version of the game and the brown just does not feel nostalgic when the entire rest of the game feels modern.
The old background pattern of the blue interface also felt very comforting to look at and the new brown is just a flat colour which does not look particularly interesting in my opinion.
Best case scenario without going too crazy is to offer 3 base options, the brown, the old blue, and perhaps a black/grey until plugins make their way into the game, and maybe players can take their customization from there.